I just thought of the best analogy for ska.

Ska is like a tree

First wave is the roots, sucking in different sounds and cultures like nutriants.

Second wave is the trunk of the tree, it is what holds everything together, with out it ska would still be underground.

Third wave is all the branches. they're all coming from the same source but going in different directions. (ska-core, ska-punk, etc.)

What do you think of that?